I don't expect the joy of crushing one's enemies to be stable under reflection.

I expect the joy of crushing one's enemies to be very stable since it matches the biologically hardwired incentives: you want to perpetuate your genes, not the genes of your neighbour.

crushing them probably seems less like a good idea, on the grounds that the badness of the subjective experience of suffering being crushed shouldn't depend on whether that experience gets implemented in your own skull or somewhere else (e.g., your enemy's skull)

Boggle. Have you, um, looked around at empirical reality? You can theorycraft about perfectly compassionate bodhisattvas who treat the suffering of each sentient as their own, but in the world I live in people crush each other's skulls for power and wealth on a very very regular basis (sometimes with clubs and sometimes with drones) and such practices don't seem to be going away.

The mainstay of government power -- including in the West -- is still the explicit threat of violence. If you piss off the government enough, men with guns will come and force you into compliance. These men are very clear about the difference between your suffering and their suffering.